Application of Solid-Phase Extraction for Trace Elements in Environmental and Biological Samples: A Review

4D-Printed Elution-Peak-Guided Dual-Responsive Monolithic Packing for the Solid-Phase Extraction of Metal Ions

Four-dimensional printing (4DP) technologies are revolutionizing the fabrication of stimuli-responsive devices. To advance the analytical performance of conventional solid-phase extraction (SPE) devices using 4DP technology, in this study, we employed N-isopropylacrylamide (NIPAM)-incorporated photocurable resins and digital light processing three-dimensional printing to fabricate an SPE column with a [H+]/temperature dual-responsive monolithic packing stacked as interlacing cuboids to extract Mn, Co, Ni, Cu, Zn, Cd, and Pb ions. When these metal ions were eluted using 0.5% HNO3 solution as the eluent at a temperature below the lower critical solution temperature of polyNIPAM, the monolithic packing swelled owing to its hydrophilic/hydrophobic transition and electrostatic repulsion among the protonated units of polyNIPAM. These effects resulted in smaller interstitial volumes among these interlacing cuboids and improvements in the elution peak profiles of the metal ions, which, in turn, demonstrated the reduced method detection limits (MDLs; range, 0.2-7.2 ng L-1) during analysis using inductively coupled plasma mass spectrometry. We studied the effects of optimizing the elution peak profiles of the metal ions on the analytical performance of this method and validated its reliability and applicability by analyzing the metal ions in reference materials (CASS-4, SLRS-5, 1643f, and Seronorm Trace Elements Urine L-2) and performing spike analyses of seawater, groundwater, river water, and human urine samples. Our results suggest that this 4D-printed elution-peak-guided dual-responsive monolithic packing enables lower MDLs when packed in an SPE column to facilitate the analyses of the metal ions in complex real samples.

Tuning the fabrication of knotted reactors via 3D printing techniques and materials

Although three-dimensional (3D) printing technologies can customize a diverse range of devices, cross-3D printing technique/material comparisons aimed at optimizing the fabrication of analytical devices have been rare. In this study, we evaluated the surface features of the channels in knotted reactors (KRs) fabricated using fused deposition modeling (FDM) 3D printing [with poly(lactic acid) (PLA), polyamide, and acrylonitrile butadiene styrene filaments], and digital light processing and stereolithography 3D printing with photocurable resins. Also, their ability to retain Mn, Co, Ni, Cu, Zn, Cd, and Pb ions was evaluated to achieve the maximal sensitivities of these metal ions. After optimizing the techniques and materials for 3D printing of the KRs, the retention conditions, and the automatic analytical system, we observed good correlations (R > 0.9793) for the three 3D printing techniques in terms of the surface roughnesses of their channel sidewalls with respect to the signal intensities of their retained metal ions. The FDM 3D-printed PLA KR provided the best analytical performance, with the retention efficiencies of the tested metal ions all being greater than 73.9% and with the detection limits of the method ranging from 0.1 to 5.6 ng L^-1. We used this analytical method to perform analyses of the tested metal ions in several reference materials (CASS-4, SLEW-3, 1643f, and 2670a). Spike analyses of complicated real samples verified the reliability and applicability of this analytical method, highlighting the possibility of tuning 3D printing techniques and materials to optimize the fabrication of mission-oriented analytical devices.

Nickel hydroxide nanoflower-based dispersive solid-phase extraction of copper from water matrix

In this work, a dispersive solid-phase extraction method based on Ni(OH)₂ nanoflowers (Ni(OH)₂-NFs-DSPE) was developed to separate and preconcentrate copper ions from tap water samples for determination by flame atomic absorption spectrometry (FAAS). Ni(OH)₂-NFs was synthesized using a homogeneous precipitation technique and used as sorbent for copper preconcentration. X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used to characterize the synthesized sorbent. All experimental variables were carefully optimized to achieve a high enhancement factor of 107.5-folds with respect to the detection sensitivity of the conventional FAAS. The proposed method's analytical parameters including LOD, LOQ, and linear range were determined as 1.33 μg/L, 4.42 μg/L, and 3.0-40 μg/L, respectively. To assess the applicability and reliability of the developed method, optimal conditions were applied to tap water samples and satisfactory percent recoveries (94-103%) were obtained for the samples spiked at 20 and 30 μg/L. This validated the accuracy and feasibility of the developed method to real samples. The developed method can be described as a simple, efficient, and rapid analytical approach for the accurate determination of trace copper ions in water samples.

Search for effective eluent for Pd separation on ion-exchange sorbent before voltammetric determination

Determination of Pd traces in environmental samples is still a challenging analytical task. The aim of this study was to propose an efficient system (i.e. ion-exchange resin and eluent) for Pd elution from SPE column after the analyte preconcentration. Moreover, the search was focused on solvents that would not interfere voltammetric determination of Pd, as well as ICP-MS analysis. Five ion-exchange sorbents were compared in terms of effective Pd separation from matrix components when using different eluents. The highest recovery (up to 91%) of palladium was obtained for Dowex 1 and ammonium buffer as the eluent. This solution not only provides relatively high palladium elution efficiency but also allows both voltammetric and ICP-MS determinations, without any additional sample preparation. It was proven that the proposed procedure including SPE separation and determination with AdSV and/or ICP-MS could be used for quantitative Pd measurement in environmental samples, such as quartz sand used for the monitoring of Pd emission in the areas of high traffic density.

Recent Advances in Speciation Analyses of Tobacco and Other Important Economic Crops

Background:

Speciation analysis is defined as the analytical activities of identifying and/or measuring the quantities of one or more individual chemical species in a sample. The knowledge of elemental species provides more complete information about mobility, bioavailability and the impact of elements on ecological systems or biological organisms. It is no longer sufficient to quantitate the total elemental content of samples to define toxicity or essentiality. Thus speciation analysis is of vital importance and generally offers a better understanding of a specific element.

Discussion:

Thorough speciation scheme consisting of sampling, sample preparation, species analysis and evaluation were described. Special emphasis is placed on recent speciation analysis approaches including both direct and coupling methods. A current summary of advantages and limitations of the various methods as well as an illustrative method comparison are presented. Certain elements and species of interest are briefly mentioned and practical examples of speciation applications in tobacco and other important economic crops are also discussed.

Aim/Conclusion:

This review aims to offer comprehensive knowledge about elemental speciation and provide readers with valuable information. Many strategies have been developed for the determination of multiple elemental species in tobacco and other important economic crops. Nevertheless, it is an eternal pursuit to establish speciation methods which can balance accuracy, agility as well as universality.

Determination of Metals in Natural Waters by Inductively Coupled Plasma Optical Emission Spectroscopy after Preconcentration on Silica Sequentially Coated with Layers of Polyhexamethylene Guanidinium and Sulphonated Nitrosonaphthols

A series of complexing adsorbents is prepared by coating silica particles with linear polyhexamethylene guanidinium (PHMG) chloride followed by saturation with a number of sulphonated nitrosonaphthols reagents electrostatically retained by positively charged polymer layer. PHMG coated silica is hydrolytically stable even during treatment with 6 M HCl heated up to 50 °C. The adsorption of 1-nitroso-2-naphthol-3,6-disulfonic acid (nitroso-R-salt), 2-nitroso-1-naphthol-4-sulfonic acid (nitroso-N-salt), and 2-nitroso-1-naphthol-3,6-disulfonic acid (nitroso-K-salt) on PHMG modified silica was studied. The effective immobilisation of sulphonated nitrosonaphthols was achieved in the range of pH of 3 - 8, while the adsorption of the monosulphonated reagent (nitroso-N-salt) is twice as high as the disulphonated analogues (nitroso-R-salt and nitroso-K-salt). The adsorption of Cu(II), Fe(III), Co(II), Ni(II), Al(III), Zn(II), Pb(II), Mn(II), and Cr(III) on prepared complexing adsorbents under static and dynamic conditions was studied as a function of time, pH, sample volume, and presence of interfering ions. Metal ions can be desorbed by using 1 M HCl or 1 M HNO₃. The preconcentration factors of metals under optimized conditions are varied from 20 to 80. The developed method was used for the preconcentration of trace metals from natural waters followed by ICP-OES determination. The sub-ppb limits of detection of metals are achieved.

Preparation of a novel nano-Fe3O4/triethanolamine/GO composites to enhance Pb2+/Cu2+ ions removal

In this paper, a magnetic nano-Fe₃O₄/triethanolamine/GO composite (TEA-GO-FE) was prepared by using graphene oxide (GO), triethanolamine (TEA), and ferric chloride. The result indicates that triethanolamine acted as an important role for the growing of Fe₃O₄ and adsorption ability of composite material. The synthesis mechanism of TEA-GO-FE was investigated through the medium of SEM-EDS, XRD, FT-IR, and TEM. The characterization results indicated Fe₃O₄ nanoparticles have been successfully loaded on the surface of graphene oxide and they were encapsulated by TEA and have excellent stability. According to the results of XRD, the general particle size of Fe₃O₄ on TEA-GO-FE was 27.5 nm. In order to understand the adsorption properties of TEA-GO-FE for Pb²⁺ and Cu²⁺, this article uses a static adsorption study method. The optimized adsorption conditions are as follows: pH = 5.0, temperature is 293.15 K, and the ion concentration is 100 mg/L. Under the optimized prerequisites, the adsorption capacities of Pb²⁺ and Cu²⁺ were 121.5 mg/g and 68.7 mg/g, separately. Through thermodynamic as well as kinetic studies, the adsorption process of Pb²⁺ and Cu²⁺ on TEA-GO-FE is a self-heating process.

Comparative study of substituted poly(4-vinylbenzyl chloride/ethylene glycol dimethacrylate) sorbents for enrichment of selected pharmaceuticals and estrogens from aqueous samples

This study reports the syntheses of four polymeric sorbents based on nucleophilic substitution of Poly(4-vinylbenzylchloride/ethylene glycol dimethacrylate). Polymerization was executed by a simple thermal initiated bulk polymerization procedure. Ground polymer particles were functionalized through reaction with the nucleophiles triethylamine, imidazole, piperidine and pyrrolidine. Mixed-mode phases were characterized by infrared spectroscopy, nitrogen sorption porosimetry and potentiometric titration for determination of chloride content. Furthermore, materials were tested and evaluated for enrichment of seven pharmaceutical and endocrine-disrupting compounds at low ng mL^-1 levels. Results demonstrate that the imidazole modified sorbent led to high and constant recovery rates for nearly all tested compounds. Therefore, this polymer was further tested for applicability with two environmental samples. Spiked tap and river water showed similar results as in evaluation experiments. Moreover, the developed method was validated regarding linearity, repeatability, instrumental limits and stability of analytes according to international guidelines.

A colorimetric-dispersive solid-phase extraction method for the sensitive and selective determination of iron using dissolvable bathocuproinedisulfonic acid-intercalated layered double hydroxide nanosheets

In this research, a novel, simple, sensitive and selective method has been presented for the determination of iron using dissolvable bathocuproine disulfonic acid (BCS)-layered double hydroxides (LDHs) for dispersive solid-phase extraction (DSPE).

Engineering β-ketoenol structure functionality in hybrid silica as excellent adsorbent material for removal of heavy metals from water

A chelating adsorbent based on the chemical modification of silica by an efficient host able to capture toxic metals, is presented.

Foodomics and Food Safety: Where We Are

The power of foodomics as a discipline that is now broadly used for quality assurance of food products and adulteration identification, as well as for determining the safety of food, is presented. Concerning sample preparation and application, maintenance of highly sophisticated instruments for both high-performance and high-throughput techniques, and analysis and data interpretation, special attention has to be paid to the development of skilled analysts. The obtained data shall be integrated under a strong bioinformatics environment. Modern mass spectrometry is an extremely powerful analytical tool since it can provide direct qualitative and quantitative information about a molecule of interest from only a minute amount of sample. Quality of this information is influenced by the sample preparation procedure, the type of mass spectrometer used and the analyst's skills. Technical advances are bringing new instruments of increased sensitivity, resolution and speed to the market. Other methods presented here give additional information and can be used as complementary tools to mass spectrometry or for validation of obtained results. Genomics and transcriptomics, as well as affinity-based methods, still have a broad use in food analysis. Serious drawbacks of some of them, especially the affinity-based methods, are the cross-reactivity between similar molecules and the influence of complex food matrices. However, these techniques can be used for pre-screening in order to reduce the large number of samples. Great progress has been made in the application of bioinformatics in foodomics. These developments enabled processing of large amounts of generated data for both identification and quantification, and for corresponding modeling.

Synthesis and characterization of a new ion-imprinted polymer for the selective separation of thorium(iv) ions at high acidity

A new ion-imprinted polymer (IIP), which was synthesized with bis(2-methacryloxyethyl) phosphate as functional ligand and Th⁴⁺ as a template ion, can be used in high acidity environment.

Modified carbon nanotubes in online speciation of chromium in real water samples using hyphenated FI-FAAS

Fast preconcentrative speciation of chromium in polluted water samples using l-arginine functionalized multi-walled carbon nanotubes.

Simultaneous Enrichment of Polycyclic Aromatic Hydrocarbons and Cu(2+) in Water Using Tetraazacalix[2]arene[2]triazine as a Solid-Phase Extraction Selector

On the basis of the definite retention mechanism proven by the stationary phase for high-performance liquid chromatography, tetraazacalix[2]arene[2]triazine featuring multiple recognition sites was assessed as a solid-phase extraction (SPE) selector. The applicability of its silica support was used for the extraction of trace amounts of polycyclic aromatic hydrocarbons (PAHs) and Cu(2+) in aqueous samples, followed by high-performance liquid chromatography fluorometric and graphite furnace atomic absorption spectrometric determination. On the basis of the π-π interaction with PAHs and the chelating interaction with Cu(2+), the simultaneous extraction of PAHs and Cu(2+) and stepwise elution through tuning the eluent were successfully achieved, respectively. The SPE conditions affecting the extraction efficiency were optimized, including type and concentration of organic modifier, sample solution pH, flow rate, and volume. As a result of the special adsorption and desorption mechanism, high extraction efficiency was achieved with relative recoveries of 94.3-102.4% and relative standard deviations of less than 10.5%. The limits of detection were obtained with 0.4-3.1 ng L(-1) for PAHs and 15 ng L(-1) for Cu(2+), respectively. The method was applied to the analyses of PAHs and Cu(2+) in Xiliu Lake water samples collected in Zhengzhou, China.

On-line speciation of chromium using a modified chelating resin and determination in industrial water samples by flame atomic absorption spectrometry

Preconcentrative speciation of chromium in industrial water samples using a flow injection – FAAS system with a synthesized chelating resin in a minicolumn.

On-line solid phase extraction method based on flow injection-FAAS using 1,10-phenanthroline modified chelating resin for chromium speciation in industrial water samples

An online solid phase extraction method for the speciation of chromium in industrial water samples using flow injection-FAAS has been described.

Dispersive Liquid-Liquid Microextraction in the Analysis of Milk and Dairy Products: A Review

Dispersive liquid-liquid microextraction (DLLME) is an extraction technique developed within the last decade, which involves the dispersion of fine droplets of extraction solvent in an aqueous sample. Partitioning of analytes into the extraction phase is instantaneous due to the very high collective surface area of the droplets. This leads to very high enrichment factors and very low solvent consumption, relative to other liquid or solid phase extraction methods. A comprehensive review of the various modes of DLLME in the analysis of organic and inorganic analytes in dairy products (milk, cheese, infant formula, yogurt, and breast milk) is presented here. Dairy products present a complex sample matrix and the removal of interfering matrix components can prove troublesome. This review focuses on sample pretreatment prior to the appropriate DLLME procedure, the extraction and dispersive solvents chosen, derivatisation methods, and analytical figures of merit. Where possible, a critical comparison of DLLME methods has been undertaken. The overall suitability, and limitations, of DLLME as a sample preparation technique for dairy products has been assessed.

Magnetic solid-phase extraction based on modified ferum oxides for enrichment, preconcentration, and isolation of pesticides and selected pollutants

Recently, a simple, rapid, high-efficiency, selective, and sensitive method for isolation, preconcentration, and enrichment of analytes has been developed. This new method of sample handling is based on ferum oxides as magnetic nanoparticles (MNPs) and has been used for magnetic solid-phase extraction (MSPE) of various analytes from various matrices. This review focuses on the applications of modified ferum oxides, especially modified Fe3O4 MNPs, as MSPE adsorbent for pesticide isolation from various matrices. Further perspectives on MSPE based on modified Fe3O4 for inorganic metal ions, organic compounds, and biological species from water samples are also presented. Ferum(III) oxide MNPs (Fe2O3) are also highlighted.

Use of Pollen Solid-Phase Extraction for the Determination of trans-Resveratrol in Peanut Oils

In this study, a simple and convenient method for the determination of trans-resveratrol (TRA) in peanut oils based on pollen grain solid-phase extraction (SPE) was developed. Pollen grains were used as normal-phase SPE sorbent to separate TRA from peanut oils for the first time. As a naturally occurring material, pollen grains exhibited an excellent adsorption capacity for polyphenolic compounds due to their particular functional structures such as hydroxyl groups, saturated and unsaturated aliphatic chains with aromatics. Their stable compositions as well as adequate particle size (30-40 μm) also make them suitable for SPE. Several parameters influencing extraction performance were investigated. Coupled with high-performance liquid chromatography-ultraviolet detection (HPLC-UV), a green purification method for fast determination of TRA in peanut oils using pollen grain cartridges as sorbents was established. The linearity range of the proposed method was 10-2500 ng · g(-1) with a satisfactory correlation coefficient (r(2)) of 0.9999. The limit of detection (LOD) for TRA in peanut oils was 2.7 ng · g(-1), and the recoveries in spiked oil samples were from 70.2% to 98.4% with the relative standard deviations (RSDs) less than 4.9% (intraday) and 5.2% (interday). This method was successfully applied to the analysis of TRA in several peanut oils with different brands from local market as well as other kinds of vegetable oils.

Evaluation of ultrasound-assisted in situ sorbent formation solid-phase extraction method for determination of arsenic in water, food and biological samples

A simple and rapid ultrasound-assisted in situ sorbent formation solid-phase extraction (UAISFSPE) coupled with electrothermal atomic absorption spectrometry detection (ET-AAS) was developed for preconcentration and determination of arsenic (As) in various samples. A small amount of cationic surfactant is dissolved in the aqueous sample containing As ions, which were complexed by ammonium pyrrolidinedithiocarbamate After shaking, a little volume of hexafluorophosphate (NaPF6) as an ion-pairing agent was added into the solution by a microsyringe. Due to the interaction between surfactant and ion-pairing agent, solid particles are formed. The alkyl groups of the surfactant in the solid particles strongly interact with the hydrophobic groups of analytes and become bound. Sonication aids the dispersion of the sorbent into the sample solution and mass transfer of the analyte into the sorbent, thus reducing the extraction time. The solid particles are centrifuged, and the sedimented particles can be dissolved in an appropriate solvent to recover the absorbed analyte. After separation, total arsenic (As(III) and As(V)) was determined by ET-AAS. Several experimental parameters were investigated and optimized. A detection limit of 7 ng L(-1) with preconcentration factor of 100 and relative standard deviation for 10 replicate determinations of 0.1 µg L(-1) As(III) were 4.5% achieved. Consequently, the method was applied to the determination of arsenic in certified reference materials, water, food and biological samples with satisfactory results.

Flow-injection solid phase extraction using Dowex Optipore L493 loaded with dithizone for preconcentration of chromium species from industrial waters and determination by FAAS

An online flow injection preconcentration system for speciation of Cr(iii) and Cr(vi) based on the combination of solid phase extraction (SPE) and flame atomic absorption spectrometry (FAAS) has been described.

Selective extraction based on poly(MAA-VB-EGMDA) monolith followed by HPLC for determination of hordenine in plasma and urine samples

Hordenine is an active compound found in several foods, herbs and beer. In this work, a novel sorbent was fabricated for selective solid-phase extraction (SPE) of hordenine in biological samples. The organic polymer sorbent was synthesized in one step in the plastic barrel of a syringe by a pre-polymerization solution consisting of methacrylic acid (MAA), 4-vinylphenylboronic acid (VB) and ethylene glycol dimethacrylate (EGDMA). The conditions for preparation were optimized to generate a poly(MAA-VB-EGMDA) monolith with good permeability. The monolith exhibited good enrichment efficiency towards hordenine. By using tyramine as the internal standard, a poly(MAA-VB-EGMDA)-based SPE-HPLC method was established for analysis of hordenine. Conditions for SPE, including volume of eluting solvent, pH of sample solution, sampling rate and sample volume, were optimized. The proposed SPE-HPLC method presented good linearity (R(2)  = 0.9992) within 10-2000 ng/mL and the detection limits was 3 ng/mL, which is significantly more sensitive than reported methods. The method was also applied in plasma and urine samples; good capability of removing matrices was observed, while hordenine in low content was well extracted and enriched. The recoveries were from 90.6 to 94.7% and from 89.3 to 91.5% for the spiked plasma and urine samples, respectively, with the relative standard deviations <4.7%.